2 Former Tropical Cyclones Bring Moisture to Hawaiʻi Island

The state experienced remnant moisture from two tropical cyclones last month, according to the National Weather Service monthly rain summary report.

According to the report, the most significant rain event of the month occurred from Aug. 22 through the morning of Aug. 24 during the passage of the remnants of former Tropical Cyclone Linda. The initial rain bands affected the northeast-facing slopes of the Big Island and Maui County on August 22, then spread westward to Oʻahu and Kauaʻi on Aug. 23.

Most of the rain gages in the Kona, Kohala, and Hāmākua regions of the Big Island had near to above-average rainfall for the month of August. The highest daily total of 3.66 inches came from a CoCoRaHS observer in Hōlualoa on Aug. 25. The Hōnaunau gage, another site in Kona, recorded its highest August total in a 29-year record.

The USGS’ rain gage at Kawainui Stream had the highest monthly total of 22.70 inches (254% of average).

Overall, rainfall totals for 2021 through the end of August were near to above average at most of the gages on the Big Island. The Piʻihonua gage had the highest year-to-date total of 136.23 inches (112% of average), followed closely by Glenwood (134.28 inches, 87% of average) and Kawainui Stream (133.34 inches, 133% of average).

Gages in the Hilo, Puna, and Kau regions had near to below-average August totals.

Peak rainfall totals of 3 to 7 inches were recorded along the windward slopes of the main Hawaiian Islands. There were no reports of significant flood-related damage from this event.

August closed out with another weak surface trough passing westward to the north of the state, which once again disrupted the trade winds. Afternoon showers were able to develop over some of the leeward and interior sections of the state, but the rainfall amounts were less than an inch.

Monthly totals in these areas were less than 2 inches, but because the August averages were mostly less than an inch, even relatively modest amounts of rainfall can push the totals into above-average territory.